Art of cracking hydrocarbons



March 7, 1933. E. c. HER-THEL ART OF CRACKI NG HYDROCARBONS 1927 24 Sheets-sheet l Filed Sept. 29

mwN-TOR 7l/gene #eff/fel @GQJLJOM WM-fw ATToRNEYs Alll/ A RSS Nm. .ESQ Mk Si March 7, El C. HERTHEL l ART QR CRACKING HYDRoCARBoNs Filled sept. 29, 1927 2 sheets-sheet 2 Patented Mar. 7, 1933 UNITED .aiaf'lrzs'- PA'rENry OFFICE EUGENE C. HERTBEL, OF CHICAGO, ILLINOIS, ASSIGNOR TO SINCLAB REFINING COMPANY, OF NEW YORK, N. Y., 'A CORPORATION OF MAINE y vABIT F CRACKING HYDR'OCARBONS 4 I l v Application led September 29, 1927. Serial No. 222,912.

This invention relates to improvements in the cracking of heavier and higher boiling hydrocarbon oils, such as gas oil, for the production therefrom of lighter and lower boil- 5 ing hydrocarbon oils, such as gasoline, particularly by distillation under pressure.

The va or mixture from pressure distillation crac ing operations usually includes, in addition to vapors of the desired lighter 1o and lower boiling oils, vapors of heavier and higher boiling oils not suitable as components of the desired product but which are with advantage again subjected to the crackv ing operation, and for this reason the vapor mlxture from the cracking operation proper is usually subjected to 'a refluxing operation for separation of such heavier and higher boiling components again to be subjected to the cracking operation. As commonly car- 2'o ried out, this refluxing operation usually involves entrainment, dissolved or entrapped,l in the reflux condensate of lighter and lower boiling1 components of the va or mixture vsuitab e as components of the esired product. lThe return of such lighter and lower boiling components to the cracking operation proper in turn involves not only an objectionable tendency toward overcracking of such components with consequent loss but also an objectionable tendency toward increase in the formation of carbon. Where the reluxing operation is effected or controlled by direct introduction of more or less of the raw oil to besupplied to thecracking opera tion, this tendency toward entrainment is usually increased. v Y

The reflux condensate from such reluxing operations is usually relatively refractory with respect tothe cracking conditions prevailing in the operation, and for this reason is with advantage subjected to more severe cracking conditions. One advantageous method of handling this refractory stock, in

externall heated apparatus, is to pass it in heat excliange with the heating gases for supplying .heat to the operation while these heating gases are at highest temperature, and before they pass in heat exchange with the less refractory stock undergoing treatment, for example as described in my application 5o filed September 24, 1923, Serial N o. 664,502. The heating surfaces over which the less refractory, or more easily cracked, stock circulates may thus be protected against overheating while at the same time the more refractory stock is subjected to advantageous cracking conditions. Circulation of the more refractory stock over the heating surfaces first contacting with the heating gases also affords an important measure of protection to these heating surfaces subjected to highest temperature.

However, where the reflux condensate or the oil mixture from the refluxing operation includes .entrained lighter and lower boiling B5 components suitable as components of the desired product, any tendency toward over' cracking of such components or toward increase in the formation of carbon is accentuated by subjecting such reflux condensate or oil mixture to more severe cracking conditions. This invention provides an im- -proved operation in which such reflux condensate or oil mixture is subjected to more severe cracking conditions but in which any I such tendency is minimized by stripping suchA lighter and lower boiling components from the reflux condensate or oil mixture before it is again subjected to cracking conditions in the operation.

According to the present invention, a body of oil is. heated to a cracking temperature by circulating the oil over heating surfaces eX- ternally in Contact with heating gases, vapors including vapors of the cracked product are 85 ,taken olf from this body of oil under pressure, these .vapors are subjected to a reiluxing operation from which the vapors remaining uncondensed including vapors of the desired distillate product are discharged,

after discharge from the refluxing operation any components of thereflux condensate suitable as components of the desired product are vaporized and separated therefrom, the

' product or remaining reflux condensate stripped of such components is circulated over separate heating surfaces externally in contact with heating gases', and the heating gases for supplying heat to the operation are passed first over the last mentioned separate heating surfaces and then over` the first mentioned heating surfaces. The reflux condensate is thus subjected to more severe cracking conditions `but only after separation of lighter 'and lower boiling components the return of which might tend to involve overcracking or excessive formation of carbon.

After circulation over the heating surfaces with which the heating gases firstcontact, the resulting hot oil products may with advantage be discharged into the body of oil from which vapors are taken 0H to the refluxing operation. The refluxing operation may be effected or controlled by indirect heat exchange with some suitable medium or the refluxing operation may be effected or controlled bythe direct introduction into the vapors in the refluxing operation of raw oil to be supplied tothe cracking operation. 1n such operation, where the raw oil or part of the raw oil is introduced into the refluxing operation, the raw oil remaining unvaporized is discharged in admixture with the reflux condensate and passes therewith successively through the stripping operation for separation of lighter and' lower boiling components and then over the separate heating surfaces with which the heating gases first contact. rlhe raw oil component of such oil mixtures is free from tarry or pitchy constituents produced inthe cracking operation and therefore assists in protecting the separate heating surfaces. rl"he reiluxing operation may also be effected or controlled by the direct introduction of a part of the distillate of a fraction of corresponding character. The vaporization of lighter and lower boiling components from the redux condensate or oil mixture discharged from the refluxing operation may be effected by rehpating the reflux condensate or oil mixture or by reducing the pressure thereon and separating the components consequently vaporized or by both reheating and reducing the pressure on the reflux condensate oroil mix'- ture..

rlhe invention will be further `described in connection with the accompanying drawings which illustrate, diagrammatically and conventionally, .apparatus adapted for vcarrying out the invention, but it is intended and will be understood that this further and more detailed description and illustration are by way of exemplication and that-the invention is flux condensate and .pump 26 'to lseparating drum throughllaman@ not limited thereto. ln the accompanying' drawings:

Fig. 1 represents, in elevation and partly in section and with partsbroken away, a pressure still system adapted for carrying out one embodiment of the invention, and

Fig. 2 represents, in elevation and partly in .section and with parts broken away, a pressure still system adapted for carrying out another embodiment of the invention.

' Referring to the drawings, particularly Fig. 1, the pressure still illustrated comprises a bulk supply drum 1, a battery of heating tubes 2 arranged in the heating flue of a furnace 3, and circulating connections 4, 5 and 6 including circulating pump 7 for circulating oil from the bulk supply drum upwardly through the heating to the bulk supply drum, and an auxiliary bank of heating tubes 8 arranged in the furnace 3 in the path of the heating gases from the flrebox of the furnacein advance 0 heating tubes 2. Arranged above the bulk supply drum tower may be of ordinary openbafile construction as illustrated. Vapors escape from the bulk supply drum 1 through connection l0 into the lower -end of the reflux tower 9 and vapors remaining uncondensed f thev `1 is a reflux tower 9. This.

tubes 2 and back regulated by means of valve 16 or by means v of suitable valves arranged beyond the condenser or receiver. Connection 17 1s provided for the direct introduction of raw oil into the upper end of the reflux tower 9 and connection 20 for the introduction of raw oil into the circulating still charge through the bearings of thev circulating pump 7. Connection 21 is rovided for initially charging the still and or pumping out the still at the end of a run. Connection 22is provided for discharging pitch laden oil or tar during operation. Reflux'condensate or admixed reraw oil is discharged from the lower end ofthe reflux tower 9 throu h connection 23 to the separating drum 24. lngrom this separating drum oil is circulated through connection 25 by means. of and through the bank of heating tubes 27 and thence back tothe separating drum 2d through connection 28. Vapore from the separating connection '29,for example into the reflux tower 9 as in the apparatus illustrated in Fig. l. The.

connection l31 and by thispump is forced through connection 32. and the' circulating drum escape l through the' heating tubes 8 and thence 3m oil v'remaining unvaporized in y 24' flows to pump 30 through 85 is provided for circulating oil from the body in the bulk supply drum 1l through the heating tubes 8 while the still is being brought to operating conditions of temperature and pressure.

One convenient means for controlling the heating of the oil passing through the heating tubes 27 is illustrated in the drawings. A part of the escaping heating gases is recirculated through the blower 36 to pass again over the heating tubes 8 and the heating tubes 2 in admixture with fresh hot products of combustion from the fire-box of the heating furnace, as described in Letters Patent No. 1,574,546 andNo. 1,574,547 granted February 23, 1926, to the Sinclair Refining Company on applications of John E. Bell, and the temperature increment imparted to the oil passing through the heatingtubes 27 is controlled by withdrawing the heating 4gases so recirculated either all from in front of the heating tubes27 or all from behind these heating tubes or partly, in any required degree of division, from'in front or partly from behind these heating tubes through the adjustable dampers 18 and 19. The refluxy condensate or oil mixture from the reflux tower 9 may be reheated in an independently fired furnace as well as in the main furnace, as illustrated, for the separation of lighter and lower boiling components.

To minimize heat loss, the bulk supply drum l, the circulating connections 4, 5 and 6, the reflux tower 9, the separating drum 24, the vapor connection 10 and the return connection A23, as well as other exposed parts of the' pressure still system7 are advantageously lagged or thermally insulated.

lThe following example of an operation to produce gasoline from gas oil will serve to illustrate the operation of apparatus of the type illustrated in Fig. 1 in carrying out the invention. The pressure still is initially charged with about 8,000 .gallons of gas oil and brought tocracling conditions of temperature and pressure in the usual way, circulation from the bulk supply drum being maintained through heating tubes 8 and back to the bulk supply drum as well as through heating tubes 2 and back to the bulk supplyA drum during `this period. Whenthe still is brought to a pressure of say 150 pounds to, 200 pounds per square inch, the introduction of raw oil through connection 17 is started and as suflicient oil mixture accumulates in the separating drum 24 circulation through connection 35 is gradually cut oil", finally completely cut off, and this oil mixture is circulated through the heating tubes 8 thence into the bulk supply drum by means of pump 30. During the initial period of operation, a small amount of gas oil is kept in circulation from the separating drum 24 through the heating tubes 27 and back'to the separating drum, this amount being maintained by the addition of raw 'oil through connection 34 if necessary, and as the oil mixture from the reflux tower accumulates this' initial supply of oil to protect the heating tubes 27 during the initial period of operation is gradually displaced by the oil mixture from the reflux tower.

During the initial period of operation a small flow of raw'oil is maintained through connection 20 to cool and lubricate the bearings of the circulating pump; after .operating conditions of temperature andv pressure are reached any additional raw oil required to maintain the still -charge over that introduced through the reflux tower may also be supplied through this connection. As the introduction of raw oil through the reflux tower is begun, or` shortly before or vshortly thereafter as required if the still charge is above/'or below normal,.the discharoe of pitch laden oil or tar through connection 22 is begun. When this point in the operation is reached, for example,raw oil may be supplied at a rate in the neighborhood of 2,500 gallons per hour, distillate taken o' at a rate inthe neighborhood of 1,000 gallons per hour and tar discharged at a rate in the neighborhood of 1,500 gallons per hour.

When this point in the operation is reached, oil is in circulation from the bulk'supply drum 1 through the heating tubes 2 and back to the bulk 4supply drum, vapors including vapors of the cracked products discharged both from the heating tubes 2 and the heating tubes 8 are escaping from the bulk supply drum 1 to the reflux tower 9, vapors remaining uncondensed in the reflux tower 9 are being taken ofi to the condenser 12 to condense to form the distillate product, reflux condensate and admixed raw oil from the reflux tower 9 is being discharged into the separating drum where lighter and lower boiling components are separated by vaporization consequent to circulationof this oil through the heating tubes 27 again to escape to the reflux tower 9 through connection 29, andthe remaining reflux condensate and admixevd raw oil ,stripped of such lighter and lower boiling components is returned to the bulk supply drum 1 through the heating tubes 8. The heating-gases from the fire-box of the furnace 3 pass first over the-heating tubes 8, then over the heating tubes 2 and finally over the heating tubes 27 The re- .flux condensate- ,fromV the reflux tower .9 is thus subjected to the most sevat .trated in Fig.

vere conditions prevailing in the furnace 3 but only after separation of lighter and lower boiling components. The heating tubes 2 through which oil containing tarry or pitchy components produced in the cracking operation is circulated are at'the same time protected by the heat absorbed from the heating gases by the more refractory andcleaner oil circulating through the heating tubes 8. The operation is so continued until the regular course of operation or until shortly before this time.

The separation of lighter and lower boiling components from the reflux condensate or oil mixture from the refiux tower 9 in the separating drum 24 may be promoted by reducing the pressure on this oil or oil mixture as it 1s discharged throu h connection 23. for example by means ofvalve 37 In such operation, connection 29 instead of being arranged to discharge into the reflux tower 9 is connected to a separate condensing system.

Such a separate condensing system is illustrated in 2 and is described in connection with the discussion of that iigure. A separate condensing lsystem may also be employed in conjunction with the specific apparatus illus- 1 if the branch vapor line 29a is connected to the vapor line 29 as illustrated.- Similarly, the vaporization of lighter and lower boiling components from the reflux condensateor oil mixture from the reflux tower 9 may be effected entirely by reducing the pressureon this oil or oil mixture in many cases. rlhe apparatus illustrated in Fig. 2 is adapted for carrying out` the invention in this way.

Referring to Fig. 2, the apparatus illustrated is in many respects similar to that illustrated in Fig. 1, and to avoid duplicity of description the same or corresponding parts have been designated by the same reference character with the letter a appended. Tlhe apparatus illustrated in Fig. 2 diders from that illustrated in Fig. 1 in that means for heating oil in the .separating drum 24a are not provided and instead means are provided for maintaining this drum under a pressure lower than that prevailing in the reflux tower 9a, pressure regulating and reducing valve 37a being provided in connection 23a` for this purpose. Also, the vapors from the separating drum-24a'l are discharged through connection 29a to a separate condenser 38 and receiver 39. The operation of the apparatus illustrated in Fig. 2 is likewise in general similar to the` operation of the apparatus illustrated in Fig. .1. i

Vin carrying out the invention in the apparatusv illustrated in Fig. 2, the pressure on the reflux condensate or oil mixture discharged from` the lower end of reflux tower 9a through connection 23a is reduced as it passes valve 37a, lighter and lower boiling hydmcabon ons,

the still is to be lshut down in` the vapor connection between components ot the reflux condensate or oil mixture being vaporized as a consequence of this reduction in pressure and being separated from the reflux condensate or oilrnixture remaining unvaporized in the separating drum 24a to escape through connection 29a. This pressure drop may amount, for example, to something in the neighborhood of 5-20 pounds per square inch. The pressure in the separating drum 24a may be maintained and regulated by means of valve 40 or by means of suitable valves arranged beyond the condenser 38 or the receiver 39. A refiux `tower may also be interposed in the separating drum 24a and the condenser 38 with connections arranged to return reflux condensate to the separating drum. rihe reuxing therein may be effected by indirect heat exchange with a suitable cooling medium or by the introduction of a part of the raw oil supplied to the operation or by the introduction of a part of the distillate product. if several stocks are to be supplied to the operation some of which are more refractory than others, such refractory stocks may with advantage be supplied to the operation by d1- rect introduction into such a reflux tower. The refiux condensate or oil mixture stripped of lighter and lower boiling 'components separatedas vapo-rs in separating drum 24a is then forced through the heating tubes 8a by means of pump 30a and then into the bulk supply drum 1a through connection 32a and the circulating connections 6a. y

In one aspect, it will be apparent that the invention provides an improved method of operation in which reflux condensateseparated from the vapors produced 1n a primary` cracking operation is subjected to more severe crackingy conditions in a secondary cracking operation after separation from this reflux condensate of lighter and lower boiling components tending to involve overcracking or excessive formation of carbon under such more severe cracking conditions. While the operations more specifically 'described. including discharge of the .hot oil products from such-'secondary cracking operation into the hot oil products of such primary cracking operation is particularly advantageous, certain advantages of the invention, in this aspect, are secured where the hot oil products from the secondarycracking operation are handled separately. The hot oil products from the secondary cracking operation may, for example, be discharged into a separate vaporizing drum for the separation of vapors from unvaporized components and these vapors may be separately fractionated to recover the desired distillate product.

l claim:

1. The improvement in the cracking of which comprises heating a body of oil to a cracking `temperature by circulating the oil over heating surfaces ex-v ternally in contact with heating gases and taking od vapors therefrom under pressure, subjecting these vapors to a refiuxing operation andftaking off' from the refluxing 0 eration vapors including vapors of the dsired distillate product, separating components of the reflux condensate suitable as components of the desired distillate .product by vaporization from the reflux condensate after discharge from the refiuxing operation, thereafter passing the reflux condensate stripped of such components over separate heating surfaces externally in contact with heating gases, and passing heating gases for supplying heat to the operation first over the last. mentioned-separate heating surfaces and then over the first mentioned heating surfaces whereby the oil circulating over the last mentioned heating surfaces is heated toA a higher temperature than the oil circulating over the first mentionedV heating surfaces.

2. An improved method of cracking hydrocarbon oils, which comprises heating a body of oil to a cracking temperature by circulating the oil over heating surfaces externally in contact with heating gases and taking ofi:l

vapors therefrom under pressure, subjectingv these vapors to a refl-uxingoperation and taking off from the refluxing operation vapors including vapors of the desired distillate product, separating components of the reflux condensate suitable as components of the desired distillate product by vaporization from the reflux condensate after discharge from the refiuxing operation, thereafter circulating the reflux condensate stripped of such components over separate heating surfaces externally in contact with heating gases and back to the said body of oil, and passing heating gases for supplying heat to the operation first over the last mentioned separate heating surfaces and then over the first mentioned heating surfaces whereby the oil circulating over the last mentioned heating surfaces is heated to a higher temperature than the oil circulating over the first mentioned heatingsurfaces.

3. The improvement in the cracking of hydrocarbon oils, which comprises heating a body of oilto a cracking temperature by circulating the oil over heating surfaces ex- .y ternally in contact with heating gases and.

taking off vapors therefrom under pressure,

subjecting these vapors to a refiuxing opera-V tion and introducing raw oil into direct contact with the vapors in the refiuxing operation, taking off from the refluxing operation vapors including vapors of the desired distillate product, separating components of the admixed reiiux condensate and raw oil suitable as components of the desired distillate product by vaporization from this oil mixture after discharge from the refluxing opstripped of such components overseparate heating surfaces externally in contact with heating gases, and passing heating gases for supplying heat to the operation first over the last mentioned separate heating surfaces and then over the first mentioned heating surfaces whereby the oil circulating over the last ing the oil over heating surfaces externally in contact with heating gases and taking olf vapors therefrom under pressure, subjecting these vapors to. a refluxing 'operation and introducing raw oil into direct contact with the vapors in the refluxing operation, taking off from the refluxing operation vapors including vapors of the desired distillate product, separating components of the admixed reflux condensate and raw oil suitable as components of the desired distillate product by vaporization from this oil mixture after discharge from the refluxing operation, thereafter circulating the oil mixture stri ped of such components over separate he'atlng surfaces externally in contact with heating gases and back to the said body of (wlil, and passing heating gases for supplying eat to the operation first over the last mentioned separate heating surfaces and then ove the rst mentioned heating surfaces whereby Athe .oil A circulating over the last mentioned heatlng surfaces is heated' to a higher temperature than the oil circulating over the first mentioned heating surfaces.

' 5. The improvement in the cracking of hydrocarbon oils, which comprises heatina body of oil to a cracking temperature y circulating the oil vover heating surfaces externally in contact with heatin vgases and taking off vapors therefrom un er pressure, subjecting these vapors to a refluxing operation and taking ofi' from the refluxing operation vapors including=vapors of the desired distillate product, Vaporizing and separating. components of the reflux. condensate suitable as components of the desired distillate product therefrom by reheating the reflux condensate after discharge from the refluxing operation to a temperature higher than that at which it is discharged therefrom, thereafter passing the reiux condensate stripped ofI such components overseparate heating surfaces externally'in contact with heating gases, and passing heating gases for supplying heat to the *operationrst over the last mentioned separate heating surfaces and then over the first mentioned heating surfaces whereby the oil circulating over the last mentioned heatin'g surfaces is heated to a higher temperature eration, lthereafter passing the oil mixture via ' the operation first hydrocarbon oils, which l oil circulating over the last mentioned than the oil circulating over the rst mentioned heating surfaces.

6. The improvement in the cracking of comprises heating a body of voil to a cracking temperature by circulating the oil over heating surfaces externally in contact with'heatin gases and taking ed vapors therefrom un er pressure, subjecting these vapors to a reuxing operation and taking od from the reuxing operation vapors including vapors of the desired distillate product, vaporizing and separating components of the reflux condensate suitable as components of the desired distillate product therefrom by reducing the ressure on the redux condensate 'after disc arge from the reduxing operation, thereafter passing ateatro! the redux condensate stripped of such components to a crackin temperature by passin it over separate eating surfaces externa ly in contact with heating gases, and supplying operation by passing heating gases from the furnace rst over the last mentioned heatin surfaces and then over the first mentione heating surfaces.

In testimony my name.

EUGENE C. HERTHEL.

hereof, I- have subscribed the redux condensate stripped of such componente over separate heating surfaces externally in .contact with lheating gases, and passing heating gases for supplying heat to over the last mentioned separate heatin surfaces and then over the rst mentioned eating surfaces wherebyl tle ea ing surfaces 1s heated to a higher temperature than the oil circulating over the rst mentioned heating surfaces.

7. rlihe improvement in hydrocarbon oils, a body of oil to a the cracking Aof which comprises heating ternally in"`contact with heatin gases 4and taking od vapors therefrom under pressure, subjecting these vapors to a reduxing operation and taking off from the reiuxing operation vapors including vapors of the desired distillate product, separating components of the reiiux condensate suitable as components of the desired distillate product by vaporization from the redux condensate after discharge from the reduxing operation, and thereafter passing the reiiux condensate stripped of such components over separate heating surfaces externally in contact with heating 'gases of higher temperature than said first mentioned heating gases and thereby heatin the oil circulating over the last mention heating surfaces to a higher temperature than the oil circulating over the first mentioned heating surfaces.

8. 'llhe improvement ,in the cracking of hydrocarbon oils, whichcomprises heating a body of oil to a vcracking temperature by circulating the oil over heating surfaces externally in contact vvith heating gases and taking 0H vapors therefrom under pressure, subjecting these va and taking ed rom the reduxing operation vapors including vapors of the desired distillate product, separating components of the reflux condensate suitable as components of Y the desired distillate product by vvaporization of the redux condensate after dischar e from the reuxing operation, thereafter eating cracking temperature by v circulating the oil over heating surfaces ex.

ors to a reuxing operation o heat to the first mentioned heatingV ice 

